The Federal Communications Commission (FCC) is responsible for allocating the finite radio frequency spectrum among various government entities, cellular telephone and data carriers, and a host of competing corporate and individual interests. In that capacity, the FCC has allocated certain frequency bands for use by and for the benefit of local, state, and national public safety organizations and applications.
Referring to FIG. 1, a portion 100 of the electromagnetic spectrum, including bandwidths allocated by the FCC to public safety applications, is depicted. A frequency band 101a from 799 to 805 megahertz (MHz) has been allocated for uplink (UL) transmissions by public safety narrowband (PSNB) voice communications by police, fire, and other emergency response teams. Frequency band 101a is paired with a frequency band 101b from 769 to 775 MHz that has been allocated for downlink (DL) transmissions by such PSNB voice communications by police, fire, and other emergency response teams. These frequencies support “push-to-talk” land mobile radio (LMR) two-way radio devices used by law enforcement agencies across the country. Similarly, a frequency band 102a from 806 to 809 MHz, and a frequency band 103a from 809 to 815 MHz, has each been allocated for UL PSNB transmissions and is each respectively paired with a frequency band 102b from 851 to 854 MHz, and a frequency band 103b from 854 to 860 MHx, that has been allocated for DL PSNB transmissions.
A frequency band 104a from 793 to 798 MHz has been allocated for UL broadband public safety transmissions, for example, by police, fire, and other emergency response teams. Frequency band 104a is, in turn, paired with a frequency band 104b from 763 to 768 MHz that has been allocated for DL broadband public safety transmissions by police, fire, and other emergency response teams. The FCC has mandated the use of Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) technology in this broadband spectrum. This corresponds to the upper portion of the 3GPP evolved universal mobile telecommunications system terrestrial radio access (E-UTRA) operating band 14 of the frequency spectrum.
The FCC also has designated a frequency band 105a from 776 to 787 MHz for UL broadband transmissions, and paired with a frequency band 105b from 746 to 756 MHz for DL broadband transmissions (referred to as operating band 13, or BC13, and also expected to be LTE compliant) by public operators, such as Verizon Wireless.
Further, the FCC has designated a frequency band 106a from 788 to 793 MHz for UL broadband operations (possibly with shared access) for public safety transmissions, and has paired this with a frequency band 106b, from 758 to 763 MHz, for DL broadband operations (possibly with shared access) for public safety transmissions, which also may be mandated as LTE compliant. This corresponds to the lower portion of the 3GPP E-UTRA operating band 14.
Because the foregoing public safety broadband spectrum allocations are spectrally near the PSNB voice band, some of the energy from the broadband allocations may “leak” into a PSNB network. Under certain conditions, this leakage, known as out-of-band emissions (DOBE), may cause undesirable radio interference to communications between an LMR base station and one or more of LMR mobile devices, for example, resulting in desensitization of a receiver of the LMR mobile device, particularly when the LMR mobile device is geographically co-located (for example, in the same police car or fire truck or even in a same radio) with the interfering broadband radio/mobile device. Those skilled in the art will appreciate that base stations and vehicular radio frequency tuning equipment can employ cavity filters that can selectively determine a desired frequency range to be transmitted; however, such cavity filters are expensive and typically cannot eliminate OOBE entirely and, further, are too large for use in handheld products.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions and/or relative positioning of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention. It will further be appreciated that certain actions and/or steps may be described or depicted in a particular order of occurrence while those skilled in the art will understand that such specificity with respect to sequence is not actually required. Those skilled in the art will further recognize that references to specific implementation embodiments such as “circuitry” may equally be accomplished via replacement with software instruction executions either on general purpose computing apparatus (e.g., CPU) or specialized processing apparatus (e.g., DSP). It will also be understood that the terms and expressions used herein have the ordinary technical meaning as is accorded to such terms and expressions by persons skilled in the technical field as set forth above except where different specific meanings have otherwise been set forth herein.